In Caucasian populations, skin cancers, when grouped together, form the most commonly diagnosed human malignancy. Skin cancers are named after the type of cells that it is derived from. The three most common skin cancers are basal cell carcinomas, squamous cell carcinomas and melanomas in descending order of frequency. The first two comprise the majority of skin cancers and carry low morbidity and mortality, whilst melanomas are associated with a much higher degree of mortality due to its propensity to metastasize.
This revision article aims to give an overview of the different types of skin cancer, and will be covering the following areas:
UVB (B for Burn and Bad):
- Very important in both sun burn + development of skin cancer.
- Increasing importance in development of skin cancer.
- Causes tanning but not sunburn.
- Also important in those with photosensitivity.
Short Term effects
Long term effects
This classification is important as it dictates the populations that may be more prone towards developing skin cancers. For example, individuals with Type 1 skin has the least protection from the sun's ultraviolet rays, and has the highest risk of developing skin cancer compared to other skin types.
Types of skin cancer:
The main risk factor for most skin cancers is exposure to UV radiation in the absence of adequate melanin pigmentation. Other risk factors specific to each type of cancer will be covered later on.
Locations on body:
Squamous cell carcinomas and actinic keratosis tend to occur at sites of high UVR exposure. Important areas include:
Basal cell carcinomas are most commonly found on the face.
Melanomas are more commonly found on areas of intermittent sun exposure. This includes on the legs, back, under the nails and soles of feet. However, pigmentation on nail beds may also obscure an underlying melanoma; a high-index of suspicion is needed when diagnosing and managing pigmented skin lesions.
1) Actinic keratoses are small, red, scaly, areas on sun-exposed sites - they signify areas of dysplasia.
If an actinic keratosis rapidly increases in size, ulcerates, bleeds or becomes painful, suspect that the lesion may have transformed to an SCC.
2) Bowen's Disease - slow-growing, reddish-brown, scaly lesions, often on the legs. These are areas of full-thickness dysplasia, which may lead to SCCs. It is an important differential diagnosis of BCC.
Curettage - Remove and send for histological assessment
This is the most common human skin cancer. It is 5 times more prevalent compared to SCCs, and arises from the basal cells in the epidermis of the skin.
The history – usually “Nodular” (see image to right).
Diagnosis - Mainly clinical, but if in doubt, histological examination of the biopsied lesion may confirm the diagnosis
BCCs may also be categorised as follows:
2. Morphoeic / Sclerosing
Management of BCCs:
The excised area is examined under the microscope to ensure that the entire lesion has been removed. If the tumour reaches the margin of the excised lesion, the dermatologist may opt to excise further, or observe the area closely.
Cure rate is >85%.
Common sites (sun-exposed surfaces):
Diagnosis - If an SCC is suspected, a biopsy is taken for histological confirmation. The histology report will include the degree of differentiation, the depth of the tumour and the margins of the excised specimen.
Prognosis depends on the site and the cause. There is a lower risk of metastatises if the cause is UV radiation, and it is not on the lip or ear. There is a higher risk of metastasis if the tumour occurs on a non sun-exposed area, and the risk is highest if it developed from Bowen's disease or a chronic ulcer.
"In transit" metastases involves a locally spreading the tumour, which is discontinuous with the primary site.
Definition: Cancer of melanocytes, which are cells in the basal layer of the skin producing melanin. The number of melanocytes in both black and white people are similar, but the amount of pigment made varies.
High mortality– 20%
The following 3 types start with a horizontal growth phase occuring in the epidermis layer (This appears as an enlarging, pigmented macule/plaque that is considered "in situ"), before the vertical phase begins – at which point the cancer becomes invasive.
1) Superficial spreading
2) Lentigo Maligna
3) Acral Lentiginous Melanoma:
These 3 types tend to grow slowly until the vertical phase begins. At this point, they start to thicken and develop into a nodule. The timing at which this phase begins is unpredictable.
The other types of melanomas have no horizontal phase – they develop as a pigmented nodule. The main type is thenodular melanoma:
To describe or diagnose a suspected melanoma, the following acronym “ABCDE” may be applied:
A – Assymmetry
B – Border irregularity
C – Colour variation
D – Diameter >6mm
E – Evolving – enlarging or changing?
Having more of these features strengthens the suspicion of the lesion being a melanoma
Breslow's depth is used as a prognostic factor, and describes the depth of invasion of the tumour cells. The depth is calculated by evaluating the entire tumour obtained through excisional biopsy.
Excision according to the Breslow Thickness Score is the gold standard. Breslow thickness is a reliable, widely-used measurement to guide the adequacy of the margins of the excised lesion. For example:
Clark’s levels is another measurement that can be used, which measures the layer of skin the melanoma has spread down to.
Normally the excision is done in 2 stages. Firstly, to remove the lesion under local anaesthetic. This is sent for histology to confirm a melanoma and its thickness. Then the another excision is carried out to remove the margin.
Following excision, regular checkups are required.
http://www.dermnet.com/ - Large database of images for skin cancers and other skin diseases.
Gawkrodger D. Dermatology: An Illustrated Colour Text. Churchill Livingstone; 4 edition.
Breslow A. Thickness, cross-sectional areas and depth of invasion in the prognosis of cutaneous melanoma. Ann Surg 1970; 172:902
Clark, W.H., Jr.: A classifiation of malignant melanoma in man correlated with histogenesis and biologic behavior. In Montagna W, Hu F (eds): Advances in Biology and Skin, Vol 8, The Pigmentary System, Pergamon Press, New York, 1966: 612-647
Fitzpatrick TB: Soleil et peau. J Med Esthet 1975;2:33034.
With thanks to disease-picture.com for allowing the use of their images in the production of this revision article.
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